The influence of finasteride on the volume of the peripheral and periurethral zones of the prostate in men with benign prostatic hyperplasia

To determine the influence of androgen deprivation induced by the potent 5α‐reductase inhibitor finasteride on the volume of the zones of the prostate, 20 symptomatic men with established BPH were randomized to one of three groups: placebo, finasteride 1 mg, and finasteride 5 mg/day. The volume of the entire prostate gland, periurethral zone, and peripheral zone and the seminal vesicles were determined by three dimensional reconstructions of magnetic resonance contoured images of the prostate. There was no significant difference between the results achieved with 1 and 5 mg of finasteride per day; thus the results in these two groups were combined. In the placebo group there was no significant change in the volume of any structure. Following treatment for 1 year with finasteride there was a significant (P <0.02) 17% decrease in total gland size (11.5 ± 3.2 cc). Similarly, there was a significant (P <0.03) decrease in the size of the periurethral zone of the prostate (6.2 ± 3 cc). Although there was also a decrease in the size of the peripheral zone of the prostate (2.8 ± 1.2 cc) this did not reach statistical significance. There was no significant change in the volume of the seminal vesicles. These findings indicate for the first time that androgen deprivation induces a significant decrease in the size of the periurethral zone of the prostate in men with established BPH. © 1993 Wiley‐Liss, Inc.